The present invention relates to flyback transformers for supplying an anode voltage to a cathode-ray tube (hereinafter referred to as a "CRT") display device such as a TV image receivers or the like, and more particularly to a flyback transformer which is capable of reducing leakage of magnetic flux.
The CRT display devices which are used as TV receivers or display terminal devices for computers or the like, have several parts or components, for example, flyback transformers for supplying an anode voltage to the CRT. These components generate a leakage magnetic field which leaks out to the circumferences of the CRT display. Such unnecessary electromagnetic radiation has an adverse effect upon the operation of electronic devices and equipment in the vicinity of the CRT. Furthermore, in recent research and experiments on the effect of the magnetic fields to humans and animals, this leakage magnetic field is determined to have a detrimental effect upon all living creatures.
Accordingly, various proposals for overcoming this problem have been made in the prior art. To assist a full understanding of the present invention, the nature and limitations of the flyback transformers of the prior art will first be described with respect to typical examples thereof and with reference to FIGS. 1 to 2D of the accompanying drawings, which will be briefly described hereinafter.
As shown in FIG. 1, a conventional flyback transformer 1 has a pair of U-shaped magnetic cores 2 and 3 respectively having leg portions 2a, 2b, 3a and 3b which are in a mutually opposing state. The mutually confronting leg portions 2a and 3a on one side are inserted into a common conductor winding (hereinafter referred to as a coil) 5. The end surfaces of the leg portions 2a and 3a on one side and the portions 2b and 3b on the other side respectively face each other to thus form a rectangular magnetic path. In order to prevent the saturation of the cores 2 and 3, gap spacers 4a and 4b are inserted between the above mentioned facing end surfaces, thereby forming gaps 6a and 6b therebetween.
In the case where the gaps 6a and 6b are formed in the manner between the end surfaces of the core leg portions, magnetic flux leaks from the gap 6b formed outside of the coil 5. This leakage flux not only has an adverse effect on various electronic components installed around the flyback transformer but also leaks out of the apparatus to become a cause of various deleterious effects.
Accordingly, as a measure for reducing these undesirable effects, a flyback transformer 1X as illustrated in FIG. 2A has been proposed in Japanese Utility Model Application Laid-open Publication No. 61-79511 (1986). The flyback transformer 1X has a pair of U-shaped cores 2X and 3X wherein the leg portions 2a and 3a on the side of a coil 5 are made slightly shorter than the leg portions 2b and 3b on the other side, to thereby form a rectangular magnetic path. In the gap between the mutually confronting leg portions 2a and 3a on the side of the coil 5, a gap spacer 4X is inserted in a collective manner. The mutually confronting leg portions 2b and 3b outside of the coil 5 are placed into intimate abutting contact. By the construction of the flyback transformer 1X, the leakage of flux from the abutting portions of the leg portions 2b and 3b is greatly reduced.
In the flyback transformer 1X as shown in FIG. 2A, it is necessary to use a gap spacer 4X having a thickness which is approximately twice that of each of the gap spacer 4a and 4b inserted into the gaps 6a and 6b of the flyback transformer 1 shown in FIG. 1. For this reason, as shown in FIG. 2B, the expansive bulging of the outer side of the main magnetic flux 7 from the gap 6X within the coil 5 increases. This causes a temperature rise of conductors (windings) in the vicinity of the gap 6X. This phenomenon, which has been described in detail in Japanese Utility Model Application Laid-open Publication No. 61-5786 (1986), will now be considered in conjunction with FIGS. 2A and 2B.
In FIG. 2B, reference numerals 5a to 5f designate cross sections of the electroconductor wire forming the coil 5. Each pair of the cross sections 5a and 5b, 5c and 5d, and 5e and 5f represent the upper and lower ends, respectively, of the same winding loop. The direction of the electric current flow is indicated by the conventional symbols and . The symbol indicates that the current is flowing away from the viewer. The symbol indicates the opposite current direction, i.e., towards the viewer. As the result of the current flow successively through these wire loops, magnetic flux is generated around the wire of each loop as indicated by the intermittent arc arrows. These small fluxes are aggregated as a group, whereby a magnetic flux 8 circulates around the cores 2X and 3X. At the portion of the gap 6X, the main flux 7 assumes an expansive bulged state on the outer side at its two ends.
A small magnetic flux is generated around the wires 5c and 5d of the coil 5 interposed between the two ends of the main magnetic flux 7 as described above. The direction of the small flux is reverse to that of the main magnetic flux 7. For this reason, the wire part 5a and 5d is completely meaningless when viewed from the coil 5 as a whole. As a matter of fact, this wire part reduces the main magnetic flux 7. As a consequence, reduction of inductance and increase in coil copper loss occur. Thus the temperature of the wire in the vicinity of the gap 6X is caused to rise. When the temperature of one part of the coil 5 rises locally in this manner, there is the undesirable possibility of reduction of the serviceable lives of the flyback transformer itself and of the electronic components installed therearound.
In the operation of the flyback transformer of the above described construction, it is true that the leakage of flux from the part of the gap 6X can be reduced, it being
possible to decrease the leakage of flux from 1/4 to 1/5 of that of the prior art example shown in FIG. IA. However, as indicated in FIGS. 2C and 2D, the leakage flux 9 from the cores 2 and 3 and the coil 5 is large. Consequently, this construction is inadequate as a solution to the requirement for reducing the leakage magnetic field with reference to flyback. For this reason, it has been the practice in the prior art to insert the flyback transformer 1X into a shield case or to encase the entire chassis (not shown) of the CRT display within a metal shield.
However, the shortening of the serviceable life of the flyback transformer due to local overheating of the coil and the various measures described above entail extremely high cost. Moreover, the productivity of the CRT display deteriorates. At the same time, the temperature of the chassis part rises and gives rise to problems such as frequency performance failures.